1. Field of the Invention
This invention relates to full duplex transceiver systems and more particularly to frequency translation in transceiver systems involving bidirectional frequency translation.
2. Background of the Invention
Many radios are of the type that employ separate circuit stages for multiplexing and frequency translation for separating receive signals from transmit signals and for translating low frequency signals into radio frequency or high frequency bands. The use of separate circuit stages for multiplexing and frequency translation introduces a distortion in the form of phase error and group delay and distortion due to unwanted coupling. Additionally the use of separate circuit stages imposes a cost associated with the components used to implement the stages, and also imposes enclosure size limitations, power supply requirements and power dissipation considerations. In addition, the number of energy leakage paths in the system is determined by the number and placement of components.
Also, in a transceiver, frequency separation between transmit and receive frequencies is used to isolate separate transmit and receive frequency spectra. This is often accomplished using separate transmit and receive signal paths having respective up/down frequency translation stages. This leads to a redundancy in frequency translation components as similar components are used for each path. A reduction in components can be achieved by switching one up/down frequency translation stage selectively in and out of the transmit and receive paths but this defeats full duplex operation, reducing the system to half duplex operation only.
Thus, it would be desirable to achieve simultaneous up/down frequency translation in a single stage and reduce the number of circuit stages or reduce the number of components used in achieving multiplexing and frequency translation.